Organopolysiloxane fluids have been widely used for viscous fluid coupling because this application requires a fluid that exhibits such properties as a suitable viscosity, a high flash point, stability against oxidative and thermal degradation, and a low viscosity variation as a function of temperature.
However, due to the heat that develops as a result of the severe shear and friction that are generated in fluid coupling service, an organopolysiloxane fluid used by itself will deteriorate. For example, it will suffer from a viscosity rise or gelation after a particular period of time, and as a consequence it will lose its fluid-coupling function.
In response to this, the addition of various types of oxidation inhibitors to organopolysiloxane fluids has been investigated for the purpose of suppressing this deterioration. For example, Japanese Patent Publication Number Sho 55-18457 [18,457/1980] and U.S. Pat. No. 4,515,702 teach that dimethylpolysiloxane compositions having a small viscosity increase at high temperatures can be obtained by adding to dimethylpolysiloxane fluids a dimethylpolysiloxane with a low degree of polymerization that has been modified by an aromatic amine compound.
In each of the dimethylpolysiloxane compositions produced by the above-described methods, the aromatic amine-modified dimethylpolysiloxane undergoes a rearrangement reaction with the base oil dimethylpolysiloxane fluid under high temperatures in combination with high shear forces. This results in a decline in the viscosity of the dimethylpolysiloxane fluid itself. Thus, the application of such compositions to viscous fluid coupling is encumbered by a decline in the torque transmission ratio and a loss of fluid-coupling function.
Moreover, the cost of these methods is driven up by the complex procedure that is required in order to synthesize the aromatic amine-modified dimethylpolysiloxane.
It is an object of the instant invention to show a viscous fluid coupling organopolysiloxane composition that is capable of withstanding long-term use under high-temperature, high-shear conditions with little increase or decrease in viscosity and almost no torque fluctuation.